B+-tree indexes with hybrid row identifiers in Oracle8i

Most commercial database systems support B⁺-tree indexes using either: physical row identifiers, for example, DB2; or logical row identifiers, for example, NonStop SQL. Physical row identifiers provide fast access to data. However, unlike logical row identifiers, they need to be updated whenever the row moves. This paper describes an alternate approach where hybrid row identifiers are used. A hybrid row identifier consists of two components: a logical component, namely, the primary key of the base table row; and a physical component, namely, the database block address (DBA) of the row. By treating the DBA as a guess regarding where the row may be found, performance comparable to physical B⁺-tree indexes is attained for valid guess-DBAs. This scheme retains the logical index advantage of avoiding an immediate index update when the base table row moves. Instead, an online utility can be used to lazily fix the invalid guess-DBAs. This scheme has been used to implement B⁺-tree indexes for Oracle8i index-organized tables (primary B⁺-tree like structure) which encounter both row movement and table reorganization